1. Field of the Invention
The present invention relates to a multi-air conditioner having a plurality of outdoor units and indoor units, and more particularly, to a multi-air conditioner which enables to equally distribute a refrigerant and oil by providing a pressure equalizing pipe for connecting the outdoor units and improves operational stability, reliability and efficiency by equally using components of the outdoor units.
2. Description of the Background Art
As for general air-conditioners, there is what is called a heat pump or an air conditioner for four seasons which is designed to allow the flow of a refrigerant to be reversed and thus capable of both cooling and heating.
Meanwhile, a multi-air conditioner is provided with indoor units respectively disposed at a plurality of indoor spaces and with a plurality of outdoor units generally in order to effectively cope with a partial load meaning that only some of the indoor units are operated. Researches have been made with regard to connection structures of refrigerant conveying conduits in such a plurality of indoor units and outdoor units. As one example, a multi-air conditioner provided with a pressure equalizing pipe connecting between the outdoor units is disclosed in U.S. Pat. No. 5,279,131. FIGS. 1 and 2 show an air conditioner disclosed in U.S. Pat. No. 5,279,131.
Firstly, as shown in FIG. 1, the conventional multi-air conditioner is provided with a plurality of indoor units 2A, 2B, 2C and 2D and a plurality of outdoor units 1A and 1B. Each of indoor units 2A, 2B, 2C and 2D is provided with a liquefied refrigerant conduit 32 and a gasified refrigerant conduit 42. The liquefied refrigerant conduit 32 and the gasified refrigerant conduit 42 are connected with a liquefied refrigerant conduit 31 and a gasified refrigerant conduit 32 which are provided to a plurality of outdoor units 1A and 1B, respectively. The outdoor units 1A and 1B are connected together by means of a pressure equalizing pipe 9 and an oil equalizing pipe 10 in order to prevent imbalances of oil fed to compressors of the respective outdoor units 1A and 1B.
FIG. 2 is an enlarged view showing a connection relationship between the conventional outdoor units. As shown therein, a compressor 11 of the outdoor unit 1A is connected with an oil separator through a discharge pipe 20. The oil separated in the oil separator 21 returns to the compressor 11 through an oil returning pipe 22 connected with the compressor. The other outdoor unit 1B has the same structure as this. The pressure equalizing pipe 9 and the oil equalizing pipe 10 are connected between the oil separators 21 of each of outdoor units 1A and 1B to prevent imbalances of oil between the compressors 11.
An operation of such conventional multi-air conditioner is as follows.
In a cooling operation, a refrigerant takes indoor heat away from the indoor units 2A, 2B, 2C and 2D including indoor exchangers and moves to the outdoor units 1A and 1B through the liquefied refrigerant conduit 3 and the gasified refrigerant conduit 4. At this time, the refrigerant keeps low-pressure. The pressure of the refrigerant is increased in the compressors 11 provided to the outdoor units and so the high-pressure refrigerant exchanges the heat with the outdoor in the heat exchangers (not shown) of the outdoor units. After that, the pressure of the refrigerant drops in an expansion valve (not shown) and thus the refrigerant becomes low-pressure again. The low-pressure refrigerant circulates again to the indoor units.
In a heating operation, a refrigerant having emitted the heat to the indoor in the indoor exchangers moves to the outdoor units 1A and 1B, keeping high-pressure. The refrigerant which has become low-pressure in the expansion valve (not shown) exchanges the heat with the outdoor in the heat exchangers of the outdoor units 1A an 1B, and then moves to the compressor 11. The refrigerant whose pressure is increased circulates again to the indoor units.
Since the conventional multi-air conditioner in which the pressure equalizing conduit 9 and the oil equalizing conduit 10 communicate with each other between the oil separators 21 of the outdoor units 1A and 1B serves only to equalize the pressure of the high-pressure refrigerant in cooling/heating, it has problems as follows.
Firstly, in the heating operation, efficiency of a system is decreased due to uneven frosting since differences occur where the refrigerant becomes low-pressure between the outdoor units. In addition, in case there is a difference in a capacity of the compressors of the outdoor units or there are outdoor units in which compressors are not operated, operational stability and reliability of a system are decreased due to unequal distribution of the refrigerant and the oil.
Moreover, the pressure of the refrigerant is sharply increased where the refrigerant becomes high-pressure in the outdoor units being operated in the cooling operation, which may cause a damage to the compressors.
In addition, when some of the outdoor units are operated in both cooling and heating, elements being operated can be overloaded, and besides components cannot be evenly used.